Zika is a disease caused by Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis. The illness is usually mild (not severe enough to require hospitalization or result in death), with symptoms appearing 2 to 7 days after being bitten by an infected mosquito and lasting for several days to a week. However, there have been reports of serious birth defects, namely microcephaly, and other poor pregnancy outcomes in babies of mothers who were infected with Zika virus while pregnant. There have also been cases of Guillain-Barré syndrome (GBS) reported in patients following suspected Zika virus infection. GBS is a rare disorder where a person's own immune system damages the nerve cells, causing muscle weakness and sometimes, paralysis. These symptoms can last anywhere from a few weeks to several months, although some people have permanent damage and, in rare cases, GBS may result in death.
Zika virus is a member of the virus family Flaviviridae, and is thus related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses. Like other members of the Flavivirus genus, Zika contains a positive single-stranded genomic RNA, encoding a polyprotein that is processed into three structural proteins (the capsid (C), the precursor of membrane (prM) and the envelope (E)) and seven nonstructural proteins (NS1 to NS5).
Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito (A. aegypti and A. albopictus). These are the same mosquitoes that spread dengue and chikungunya viruses. These mosquitoes typically lay eggs in and near standing water in things like buckets, bowls, animal dishes, flower pots and vases. They prefer to bite people, and live indoors and outdoors near people. Mosquitoes that spread chikungunya, dengue, and Zika are aggressive daytime biters. They can also bite at night. Mosquitoes become infected when they feed on a person already infected with the virus. Infected mosquitoes can then spread the virus to other people through bites. Zika virus usually remains in the blood of an infected person for about a week but it can be found longer in some people.
Prior to 2015, Zika virus outbreaks occurred in areas of Africa, Southeast Asia, and the Pacific Islands. The first human Zika infection was reported in Uganda in 1964 and the virus was later isolated from humans in South East Asia. Despite this broad geographical distribution, human Zika infections remained sporadic and limited to small-scale epidemics for decades, until 2007, when a large epidemic was reported on Yap Island, a territory of the Federated States of Micronesia, with nearly 75% of the population being infected with the virus. Moreover, an outbreak of a syndrome due to Zika fever was reported in French Polynesia, in addition to several cases of Zika infection in New Caledonia, Easter Island and the Cook Islands, indicating a rapid spreading of the virus in the Pacific. Two imported cases of Zika infection of travellers from Indonesia and the Cook Islands, respectively, to Australia and two from Thailand to Europe and Canada, respectively, was described recently (see, Kwong et al. (2013) Am J Trop Med Hyg 89:516-517 Tappe et al. (2014) European communicable disease bulletin; Pyke et al. (2014) PLoS currents 6; Fonseca et al. (2014) Am J Trop Med Hyg 91:1035-1038), emphasizing the capacity of Zika to spread to non-endemic areas where the proper mosquito vector might be present.
In May 2015, the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed Zika virus infections in Brazil. Currently, outbreaks are occurring in many countries. Zika virus will continue to spread and it will be difficult to determine how and where the virus will spread over time.
On Jan. 22, 2016, the Centers for Disease Control and Prevention (CDC) activated its Emergency Operations Center (EOC) to respond to outbreaks of Zika occurring in the Americas and increased reports of birth defects and Guillain-Barré syndrome in areas affected by Zika.
In Feb. 1, 2016, the World Health Organization declared a Public Health Emergency of International Concern (PHEIC) because of clusters of microcephaly and other neurological disorders in some areas affected by Zika.
On Feb. 8, 2016, CDC elevated its EOC activation to a Level 1, the highest level.
As of Feb. 17, 2016, in the United States, 84 cases of travel-associated Zika virus disease cases have been reported. With the recent outbreaks, the number of Zika cases among travelers visiting or returning to the United States will likely increase. These imported cases could result in local spread of tile virus in the United States.
There is currently no available vaccine to prevent or treat Zika infection. Accordingly, the identification of novel antigens that are capable of eliciting an immune response against Zika to provide protection against infection is desirable.